Sanitaryware manufacturers often employ prevalent slip casting processes for the manufacture of china fixtures such as toilets, lavatories and pedestals. In general, during a slip casting process, the manufacturer prepares a slurry, or “slip”, by combining clay powder in a suspending liquid. The caster adds deflocculants (for instance, sodium silicate, sodium carbonate or a combination thereof) to the slurry for stability and density and further adds binders to provide further structural strength to the resulting cast. The manufacturer derives the slip from one or more clay recipes, taking into consideration factors such as material price, casting rate, consistency (with respect to particle size, surface area, casting rate, viscosity and gel structure formation), purity and low deflocculant demand. The manufacturer may vary the slurry's chemical composition to attain desirable aesthetic and performance characteristics in the finished product and also to meet the particular operating parameters of the manufacturer's equipment and casting techniques.
The caster subsequently introduces liquid slip into a mold either by gravity or by pressure from a pump. The mold sections are made from plaster of Paris or similar porous material that enables capillary absorption of water from the slip. The capillary action of the plaster mold draws the water out of the slip, and the remaining clay forms a shell that becomes the cast piece (also known as a green piece). In pressure casting, liquid slip enters a resin filter under high pressure (typically hydraulic pressure), thereby forcing water out of the slip into the filter. The pore size of the filter material is such that the clay remains on the surface of the filter to form the cast piece. In either method, the thickness of the cast piece is dependent upon a variety of factors including, but not limited to, the chemical composition of the slip, plant temperature, relative humidity, cast time, sulfate content, viscosity of the slip (initial and build up), thixotropy (viscosity versus time), slip cake weight, filtrate weight, moisture gradient and slip temperature. Upon absorption of a sufficient amount of water, the caster removes the greenware from the molds whereupon it is dried, glazed and fired. Throughout this application, “slip casting” shall include both gravity and pressure casting methods.
Manufacturers realize several advantages with slip casting processes, such as superior mold life and recovery, the ability to finish articles while they are drying and the ability to utilize workers of similar skill level. Manufacturing methods can be changed without replacing current personnel and without significant additional investments in capital expenditures and technical expertise. Pressure casting realizes an additional productivity benefit by creating a greater product volume per square foot of manufacturing floor space.
Slip casting, however, remains a capital-intensive process. The production of sanitaryware requires significant space to accommodate a limited number of molds alongside expensive equipment maintained by highly skilled personnel. Mold making technology is often proprietary, ensuring costly reliance upon mold manufacturers to modify molds and creating consequential manufacturing delays. Also, some equipment suppliers limit the chemistry used in the slip and thereby make it difficult to find suitable slips for certain molds.
In addition, slip casting comprises several time consuming and labor-intensive aspects. The slip casting industry still depends largely upon human expertise and judgment to make improvements in casting processes. The wage rate for a skilled caster is therefore fairly high, and a long training period is required to ensure proper skill levels. Due to the large intervention of human judgement, cracks and other defects in the cast often manifest themselves in the final product. Numerous other factors inhibit the uniform production of casts, such as differences in casting times, variations in ambient temperature and humidity (wherein such variations occur among different manufacturing facilities or within a single facility) and the age and condition of the molds (as the age of the mold increases, the capillary action of the mold degrades and the mold becomes saturated with water). Although manufacturers often recover and reuse materials at the cost of associated labor and overhead, most defects that are found after firing result in lost materials and up to 30% scrap and rework for manufacturers (see Kimberly L. Petri and Alice E. Smith, “A Hierarchical Fuzzy Model for Predicting Casting Time in a Slip Casting Process”).
In order to reduce manufacturing and temporal costs inherent in most slip casting procedures, sanitaryware manufacturers have long sought enhancements in such processes, particularly due to the complex configuration of toilets and the inherent propensity for production losses. Fashionable designer products such as toilet bowls have large hollow areas comprising the shroud or shell. Large hollow areas are problematic, since the timing of the draining and setting must be consistent to avoid the appearance of cracks at the green stage.
U.S. Pat. No. 1,289,151 discloses a process of casting a toilet bowl in which the manufacturer casts a part of the bowl below a curved plane lying along the upsiphon passageway. The manufacturer simultaneously casts a portion of the bowl lying above this plane and subsequently secures the two parts to on another.
U.S. Pat. No. 1,337,663 discloses a mold for manufacturing a toilet bowl having a mold and core made of an absorbent material such as plaster. A portion of the core is covered with a nonabsorbent material to prevent formation of a crust of clay thereadjacent.
U.S. Pat. No. 1,435,644 discloses a method of constructing an earthenware bowl with a flushing rim. In the disclosed method, the bowl and outer section of the rim are formed together, the top and inner skirting of the rim are formed separately and the top of the rim is subsequently united with the upper marginal edge of the outer rim section.
U.S. Pat. No. 1,447,529 discloses a process for making a toilet having an integral bowl and base. In the disclosed process, liquid slip is poured between an external mold body and an absorbent internal mold core. The mold and core are spaced from one another by a distance equal to the thickness of the wall of the finished product. The caster inverts the mold during the pouring of the slip, thereby permitting the slip to flow laterally and form a base of the toilet subsequent to the formation of the bowl.
U.S. Pat. No. 3,218,376 discloses a method of casting a toilet bowl having an integral flushing ring. The disclosed method employs a multiple part porous mold for the bowl and flushing ring and a removable moisture-absorbent insert fitted upon a core. The fitted core is inserted into the mold so as to underlie the flushing ring when formed. Slip is poured into the mold and insert to form the bowl and flushing ring. The core is subsequently separated from the mold and insert, and the cast bowl with flushing ring is fired.
U.S. Pat. No. 3,461,194 discloses a method of casting siphonic toilet bowl with an integral flushing ring. The method includes setting up an inverted main core mold and disposing a series of separate core pieces therearound. The pieces have outwardly projecting, spaced, flexible members to form discharge passages in the cast flushing ring. The main core and pieces are assembled with a shell mold and a foot mold and slip is poured into the main core mold. Excess clay is drained from the mold after deposition of clay thereon, thereby allowing the casting to set. The main core and pieces are removed from the cast piece, wherefore the cast piece is subsequently finished, dried and fired.
U.S. Pat. No. 3,536,799 discloses a method of continuous flow casting of vitreous china articles in molds. In the disclosed method, a plurality of molds is provided, each of which includes a face part and a cover part. The molds are consecutively arranged upright in a substantially vertical plane. The horizontal axis of each mold tilts downwardly toward an inlet in the lowermost part of the mold. Slip is injected into the molds and flows through the mold during casting to an outlet defined at the highest point of each mold. After casting, the face part is removed in a horizontal plane, as is the cast product.
U.S. Pat. No. 5,268,047 discloses a method of producing toilet assemblies having different size drainpipes. In the disclosed method, a common mold is provided for molding a plurality of identical toilet bowls and a plurality of different molds are provided for molding a plurality of drainpipes of varying size. Multiple molded toilet bowls are joined with corresponding drainpipes and sealed at the joint therebetween to form a plurality of toilet bowl assemblies. The assemblies are air-seasoned, glazed and fired to produce finished assembled having drainpipes of different sizes.
U.S. Pat. No. 5,514,316 discloses a method of casting a ceramic article, wherein a porous casting mold is provided that includes a mold cavity with a green ceramic body placed thereinside. Slip is supplied to the mold cavity and forms a deposit upon an inner surface of the mold, thereby integrating the green ceramic body and the deposit into a single ceramic body. The green ceramic body and the slip are substantially the same in composition, and the water content of the green ceramic body approximates a water content of the slip so as to prevent the green ceramic body from swelling.
U.S. Pat. No. 6,428,643 discloses a method and apparatus for casting toilets in which the bowl and rim are separately molded and subsequently joined while both are inverted. During connection of the rim and bowl, two opposing sides of the mold support the bowl, and an inverted rim has slip material applied to its lower surface. A trolley raises the rim so that the bottom surface of the rim engages the top surface of the bowl when both are upside down, thereby resulting in a cast greenware toilet.
None of the aforementioned references discloses solid cast prefabricated pieces that are separately cast and subsequently assembled to produce a variety of highly complex models from a single platform. Integration of platforms in manufacturing strategies is well known in several industries for implementing common underlying structure as the basis for multiple, varying products. In the automotive industry, for instance, a “platform” refers to a vehicle's suspension, drive train and structural components. Auto manufacturers having multiple divisions use platforms to produce similar models under different nameplates, thereby supporting common design themes while satisfying consumer loyalty to specific brand names. A single manufacturer may only have four platforms yet manufacture over 30 different vehicles around the world (see www.safecarguide.com/gui/nee/types). Dependence upon platforms therefore enables auto manufacturers to market substantially similar vehicles to different market segments while recovering research and development costs.
The platform concept is similarly applicable in sanitaryware manufacturing for the manufacture of solid cast prefabricated pieces that can be assembled to produce a variety of bowl configurations from a single platform. Such a process would improve manufacturing yields and enable accelerated production of complex bowls designs by using the toilet's functional components (i.e., the trapway, jet and inlet and outlets) as the basis for a plurality of toilet models. It is desirable to modify such functional components according to the regulatory requirements and plumbing configurations of the geographic region in which the bowl is sold. Therefore, a single manufacturing facility can easily produce toilets for consumers of the region in which the manufacturing facility is located as well as for multiple global regions without substantial capital expenditures in new manufacturing facilities and new equipment to modify entire models according to local regulations and aesthetic tastes.
It is therefore desirable to provide interchangeable platforms in the manufacture of sanitaryware to achieve a plurality of design and functional combinations.